1. Field of the Invention
The present invention relates to an image forming apparatus used for a copier, a printer, a plotter and a facsimile, and more particularly, to an image forming apparatus having a particle modulator for controlling a flow of toner particles.
2. Description of the Related Art
An image forming apparatus having a particle modulator is disclosed in the U.S. Pat. No. 3,689,935. In the image forming apparatus, the particle modulator comprises an insulative layer, a reference electrode and a plurality of control electrodes. The reference electrode is one sheet formed on one side of the insulative layer. The control electrodes are independently formed on the other side of the insulative layer. Moreover, the particle modulator has apertures formed in at least one line. The apertures penetrate the above-mentioned three layers (the reference electrode, the insulative layer and the control electrode). The image forming apparatus further comprises a driving circuit for selectively applying a voltage between each of the control electrodes and the reference electrode, a toner particle supply device for supplying the charged toner particles toward the particle modulator, and a moving device for relatively moving a supporting member with respect to the particle modulator in a flow of the toner particles. In the image forming apparatus, the driving circuit selectively applies the voltage between each of the control electrodes and the reference electrode according to an image signal, thereby controlling the toner particles. Then, the toner particles pass through each of the apertures so that an image is formed on the supporting member.
There are three kinds of toner particle supply devices for supplying the charged toner particles to the vicinity of the apertures. According to the device disclosed in Japanese Laid-Open Patent Publication No. 62-248662, the toner particles are supplied to the vicinity of the apertures by rotation of a toner carry roller after the charged toner particles are held on the toner carry roller. Moreover, according to the device disclosed in U.S. Pat. No. 4,491,855, the charged toner particles are formed in a mist in an alternating electric field applied between a toner carrying member and a particle modulator and are supplied to the vicinity of the apertures. Further, according to the device disclosed in Japanese Laid-Open Patent Publication No. 58-114974, the charged toner particles are supplied to the vicinity of the apertures according to an air flow.
However, in the toner particle supply device employing the toner carry roller for supplying the toner particles to the vicinity of the apertures, an image-force and van der Waals forces by which the toner particles are held on the toner carry roller are comparatively great. Therefore, it is difficult to supply a sufficient amount of toner particles toward the vicinity of the apertures with certainty. On the other hand, there is a need to form an electric field having a strong magnetic force in order to draw the toner particles from the toner carry roller and in order to make the toner particles pass through each of the apertures. Thus, since there is a need to provide a high-voltage power supply in the image forming apparatus, the image forming apparatus becomes expensive.
Moreover, in the toner particle supply device employing an alternating electric field, there is a need to provide a high-priced high-voltage A.C. power supply. Therefore, the image forming apparatus becomes expensive. Further, the alternating electric field disturbs a control electric field which controls the toner particles such that the toner particles pass through each of the apertures, thereby forming an unclear image.
In the toner particle supply device employing an air flow, there is a need to provide a compressor for generating the air flow. Therefore, the image forming apparatus becomes complicated and expensive.